c# MongoDB分页辅助类，支持多条件查询

创建一个获取MongoDB数据库实例的类

    public class Db
    {
        private static IMongoDatabase db = null;

        private static readonly object lockHelper = new object();

        private Db() { }

        public static IMongoDatabase GetDb(string connStr, string dbName)
        {
            if (db == null)
            {
                lock (lockHelper)
                {
                    if (db == null)
                    {
                        var client = new MongoClient(connStr);
                        db = client.GetDatabase(dbName);
                    }
                }
            }
            return db;
        }
    }

创建一个操作MongDB的辅助类

    public class MongoDbHelper<T> where T : MongoBaseEntity, new()
    {
        private IMongoDatabase db = null;
        private IMongoCollection<T> collection = null;
        private readonly IOptions<MongoDBConfig> _options;

        public MongoDbHelper(IOptions<MongoDBConfig> options)
        {
            this._options = options;
            this.db = Db.GetDb(this._options.Value.ConnectionString, this._options.Value.DbName);
            this.collection = db.GetCollection<T>(typeof(T).Name);
        }

        /// <summary>
        /// 分页
        /// </summary>
        /// <param name="filter"></param>
        /// <param name="sort"></param>
        /// <param name="pageIndex"></param>
        /// <param name="pageSize"></param>
        /// <returns></returns>
        public PagingModel<T> GetPagingData(FilterDefinition<T> filter, SortDefinition<T> sort, int pageIndex, int pageSize)
        {
            var list = this.collection
                .Find(filter)
                .Sort(sort)
                .Skip((pageIndex - 1) * pageSize)
                .Limit(pageSize)
                .ToList();

            var count = this.collection.CountDocuments(filter);

            var pagingModel = new PagingModel<T>();
            pagingModel.Items = list;
            pagingModel.PageIndex = pageIndex;
            pagingModel.PageSize = pageSize;
            pagingModel.TotalRecords = Convert.ToInt32(count);
            pagingModel.TotalPages = (int)Math.Ceiling((double)count / (double)pageSize);

            return pagingModel;
        }
    }

说明：构造方法public MongoDbHelper(IOptions<MongoDBConfig> options)中的参数，是与配置文件中的MongoDBConfig节点对应的，我的项目是.net core项目。 

下面是appsettings.json配置文件部分代码：

  "MongoDBConfig": {
    "ConnectionString": "mongodb://xxx:xxx@192.168.3.240:27017",
    "DbName": "xxxDB"
  }

    public class MongoDBConfig
    {
        /// <summary>
        /// 数据库连接字符串
        /// </summary>
        public string ConnectionString { get; set; }

        /// <summary>
        /// 具体数据库名称
        /// </summary>
        public string DbName { get; set; }
    }

创建一个分页实体类

    /// <summary>
    /// 描述：分页实体
    /// 创建人：苏本东
    /// 创建时间：2019-3-5 19:05:20
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class PagingModel<T> where T : class, new()
    {
        /// <summary>
        /// 当前页码
        /// </summary>
        public int PageIndex { get; set; }

        /// <summary>
        /// 每页大小
        /// </summary>
        public int PageSize { get; set; }

        /// <summary>
        /// 总记录数
        /// </summary>
        public int TotalRecords { get; set; }

        /// <summary>
        /// 总页数
        /// </summary>
        public int TotalPages { get; set; }

        /// <summary>
        /// 每页数据
        /// </summary>
        public List<T> Items { get; set; }
    }

最后就是调用了

            FilterDefinition<ModbusData> filter = Builders<ModbusData>.Filter.Empty;
            if (request.Ip.IsNotNullAndEmpty())
            {
                //注意：Eq方法的第一个参数，大小写需要跟数据库一致，不然查询无效
                filter = Builders<ModbusData>.Filter.Eq("IP", request.Ip);
            }

            var sort = Builders<ModbusData>.Sort.Descending(c => c._id);
            var pagingModel = this._mongo.GetPagingData(filter,
                sort,
                (int)request.page,
                (int)request.limit);

ModbusData类是与MongoDB的表对应的

提供两篇文章供学习参考：

https://www.cnblogs.com/quebra/p/10202449.html

https://www.cnblogs.com/woxpp/p/6347429.html